Investigative methods of congenital complete heart block.

Congenital heart block (CHB) has been described for a century and related to the presence of maternal autoimmune disease for three decades, but little is understood about its mechanism. To explore the pathophysiology of CHB, technologies in both basic and clinical electrophysiology are being developed and applied. Human fetal rhythm is currently inferred from cardiac mechanical events by using fetal ultrasound, allowing for the detection of second and third-degree heart block. Fetal electrocardiography is being explored to assess its feasibility as a clinical tool to detect fetal first-degree block in the mid trimester. Sequential composite digital recordings from the maternal abdomen are made every 4 weeks from pregnancies at risk for congenital heart block. Filtering and averaging techniques are used to enhance the fetal signal. So far, these techniques have produced a fetal QRS complex trigger signal for use in three-dimensional fetal echocardiography. Because the human fetus cannot be studied directly, a Langendorff rabbit model of CHB has been developed. With 5-10 mL of human serum in 150-300 mL of Krebs solution, prolongation of the Wenckebach second-degree atrioventricular block cycle length occurred. This was reproduced by using serum from seven of eight CHB mothers as compared with none of six controls mothers.